In the past, designers of avionics systems have endeavored to provide systems with improved reliability and improved functionality. One example of such improvements is the incorporation of global navigation capabilities using the global positioning system (GPS). The GPS system has gained widespread acceptance across various fields of endeavor, including aviation. Global Navigation and Landing Units, GNLUs are becoming very common on new commercial air transport aircraft. These GNLUs can be used to provide enhanced lateral navigation (LNAV) and vertical navigation (VNAV) capabilities. However, it often is difficult to integrate this equipment with the many other interrelated avionics equipment on a typical existing commercial air transport aircraft. One particular example of integration is with an autopilot system. Often, complex interconnect hardware is required to couple a GNLU system with an autopilot on an existing aircraft. While these complex interconnect schemes have been used extensively in the past, for example on DC 9 aircraft manufactured by McDonnel Douglas, they also have significant drawbacks.
First of all, the system often requires t e addition of new interconnect wiring with complex logic controlled switching circuitry between the GNLU and the autopilot.
Secondly, in the DC 9 applications, as well as others, it also required expensive and time consuming changes to be made to the autopilot system itself.
Consequently, there exists a need for improvement in systems and methods for retrofitting GNLU systems with autopilots on existing aircraft.